resolve: mark it undetermined if single import is not has any bindings

Author: bvanjoi

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -355,6 +355,7 @@ impl<'a, 'b, 'tcx> BuildReducedGraphVisitor<'a, 'b, 'tcx> {
             parent_scope: self.parent_scope,
             module_path,
             imported_module: Cell::new(None),
+            indeterminate: Cell::new(true),
             span,
             use_span: item.span,
             use_span_with_attributes: item.span_with_attributes(),
@@ -869,6 +870,7 @@ impl<'a, 'b, 'tcx> BuildReducedGraphVisitor<'a, 'b, 'tcx> {
             root_id: item.id,
             parent_scope: self.parent_scope,
             imported_module: Cell::new(module),
+            indeterminate: Cell::new(false),
             has_attributes: !item.attrs.is_empty(),
             use_span_with_attributes: item.span_with_attributes(),
             use_span: item.span,
@@ -1070,6 +1072,7 @@ impl<'a, 'b, 'tcx> BuildReducedGraphVisitor<'a, 'b, 'tcx> {
                 root_id: item.id,
                 parent_scope: this.parent_scope,
                 imported_module: Cell::new(Some(ModuleOrUniformRoot::Module(module))),
+                indeterminate: Cell::new(false),
                 use_span_with_attributes: item.span_with_attributes(),
                 has_attributes: !item.attrs.is_empty(),
                 use_span: item.span,
@@ -1234,6 +1237,7 @@ impl<'a, 'b, 'tcx> BuildReducedGraphVisitor<'a, 'b, 'tcx> {
                     root_id: item.id,
                     parent_scope: self.parent_scope,
                     imported_module: Cell::new(None),
+                    indeterminate: Cell::new(false),
                     has_attributes: false,
                     use_span_with_attributes: span,
                     use_span: span,

compiler/rustc_resolve/src/ident.rs

@@ -967,6 +967,21 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
         // if it can then our result is not determined and can be invalidated.
         for single_import in &resolution.single_imports {
             let Some(import_vis) = single_import.vis.get() else {
+                // This branch handles a cycle in single imports, which occurs
+                // when we've previously captured the `vis` value during an import
+                // process.
+                //
+                // For example:
+                // ```
+                // use a::b;
+                // use b as a;
+                // ```
+                // 1. Steal the `vis` in `use a::b` and attempt to locate `a` in the
+                //    current module.
+                // 2. Encounter the import `use b as a`, which is a `single_import` for `a`,
+                //    and try to find `b` in the current module.
+                // 3. Re-encounter the `use a::b` import since it's a `single_import` of `b`.
+                //    This leads to entering this branch.
                 continue;
             };
             if !self.is_accessible_from(import_vis, parent_scope.module) {
@@ -981,6 +996,12 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                 // named imports.
                 continue;
             }
+
+            if single_import.indeterminate.get()
+                && binding.map_or(false, |binding| binding.module().is_some())
+            {
+                return Err((Undetermined, Weak::No));
+            }
             let Some(module) = single_import.imported_module.get() else {
                 return Err((Undetermined, Weak::No));
             };

compiler/rustc_resolve/src/imports.rs

@@ -173,6 +173,8 @@ pub(crate) struct ImportData<'a> {
     pub module_path: Vec<Segment>,
     /// The resolution of `module_path`.
     pub imported_module: Cell<Option<ModuleOrUniformRoot<'a>>>,
+    /// `true` if this import is indeterminate in all namespaces.
+    pub indeterminate: Cell<bool>,
     pub vis: Cell<Option<ty::Visibility>>,
     pub used: Cell<Option<Used>>,
 }
@@ -351,9 +353,9 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                     (old_glob @ true, false) | (old_glob @ false, true) => {
                         let (glob_binding, nonglob_binding) =
                             if old_glob { (old_binding, binding) } else { (binding, old_binding) };
-                        if glob_binding.res() != nonglob_binding.res()
-                            && key.ns == MacroNS
+                        if key.ns == MacroNS
                             && nonglob_binding.expansion != LocalExpnId::ROOT
+                            && glob_binding.res() != nonglob_binding.res()
                         {
                             resolution.binding = Some(this.ambiguity(
                                 AmbiguityKind::GlobVsExpanded,
@@ -794,6 +796,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                 ..
             } => (source, target, source_bindings, target_bindings, type_ns_only),
             ImportKind::Glob { .. } => {
+                import.indeterminate.set(false);
                 self.resolve_glob_import(import);
                 return 0;
             }
@@ -844,6 +847,10 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
             }
         });
 
+        if indeterminate_count < 3 {
+            import.indeterminate.set(false);
+        }
+
         indeterminate_count
     }
 

tests/ui/imports/cycle-import-in-diff-module.rs

@@ -0,0 +1,14 @@
+//@ check-pass
+
+// https://github.com/rust-lang/rust/pull/124840#issuecomment-2098148587
+
+mod a {
+    pub(crate) use crate::S;
+}
+mod b {
+    pub struct S;
+}
+use self::a::S;
+use self::b::*;
+
+fn main() {}

tests/ui/imports/shadow-glob-module-resolution.rs

@@ -0,0 +1,17 @@
+// https://github.com/rust-lang/rust/issues/124490
+
+mod a {
+    pub mod b {
+        pub mod c {}
+    }
+}
+
+use a::*;
+
+use b::c;
+//~^ ERROR: cannot determine resolution for the import
+//~| ERROR: cannot determine resolution for the import
+//~| ERROR: unresolved import `b::c`
+use c as b;
+
+fn main() {}

tests/ui/imports/shadow-glob-module-resolution.stderr

@@ -0,0 +1,23 @@
+error: cannot determine resolution for the import
+  --> $DIR/shadow-glob-module-resolution.rs:11:5
+   |
+LL | use b::c;
+   |     ^^^^
+
+error: cannot determine resolution for the import
+  --> $DIR/shadow-glob-module-resolution.rs:11:5
+   |
+LL | use b::c;
+   |     ^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+
+error[E0432]: unresolved import `b::c`
+  --> $DIR/shadow-glob-module-resolution.rs:11:5
+   |
+LL | use b::c;
+   |     ^^^^
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0432`.